It is useful, particularly in the clay industry, to have information on the physical properties of the solid phase in clay slurry. In particular, it is useful to know the percentage content of elements such as iron and potassium. The usual method of obtaining this information is for a sample of the slurry to be collected and taken to a laboratory where it is dried and analysed in the form of a dry powder. This is a time-consuming process, and does not permit continuous monitoring of the slurry.